+extern qboolean snd_threaded; // enables use of snd_usethreadedmixing, provided that no sound hacks are in effect (like timedemo)
+extern qboolean snd_usethreadedmixing; // if true, the main thread does not mix sound, soundtime does not advance, and neither does snd_renderbuffer->endframe, instead the audio thread will call S_MixToBuffer as needed